Electrical insulating oil containing a hydrotreated catalytically cracked cycle oil

ABSTRACT

The oxidative resistance of a mineral base oil useful as an electrical insulating oil but deficient in oxidative resistance is improved while the impulse strength of the oil is retained at an acceptable level, at least about 140 kv., by combining from about 80 to about 97 parts of the mineral base oil with from about 20 to about 3 parts of a hydrogen-refined light catalytic cycle stock fraction which boils above about 450* F. and below about 690* F., preferably below about 660* F., and has a 50 percent distillation point of at least about 550* F. This fraction of light catalytic cycle stock contains no more than about 1.0 weight percent of aromatic hydrocarbon compounds of at least four condensed rings. The blend of mineral base oil and catalytic cycle stock fraction contains no more than about 22 weight percent of all aromatic compounds and has no more than about 0.10 weight percent of aromatic hydrocarbon compounds of at least four condensed rings. The catalytic cycle stock fraction may be dewaxed before addition to the mineral base oil, and the resultant blend may be treated with activated earth for additional color and oxidation stability improvement.

United States Patent [72] Inventor Thomas G. Lipscomb, II Primary Examiner-Herbert Levine Baytown, Tex. Att0rneySTh0mas B. McCulloch, Melvin F. Fincke, John S. [21] Appl. No. 14,986 Schneider, Sylvester W. Brock, Jr., Kurt S. Myers and [22] Filed Feb. 27, 1970 Timothy 1. Burgess [45] Patented Nov. 2, 1971 [73] Assignee Esso Research and Engineering Company ABSTRACT: The oxidative resistance of a mineral base oil [54] ELECTRICAL INSULATING OIL CONTAINING A useful as an electrical insulating oil but deficient in oxidative HYDROTREATED CATALYTICALLY CRACKED resistance is improved while the impulse strength of the oil is CYCLE OIL retained at an acceptable level, at least about 140 kv., by com- 21 Claims, 1 Drawing Fig. bining from about 80 to about 97 parts of the mineral base oil with from about 20 to about 3 parts of a hydrogen-refined [52] U.S.Cl 2201235164; light catalytic cycle stock fraction which boils above about 511 Int. Cl ..c10 23/00, and helm 't belw "01b 3/22 F., and has a 50 percent distillation point ofat least about 550 50 Field of Search 208/14 19 This light caalyic Smk than about 1.0 weight percent of aromatic hydrocarbon compounds of at least four condensed rings. The blend of mineral [56] References Cited base oil and catalytic cycle stock fraction contains no more UNITED STATES PATENTS than about 22 weight percent of all aromatic compounds and 3 095 366 6/1963 Schi 208,14 has no more than about 0.10 weight percent of aromatic 2, M1967 A keman hydrocarbon compounds of at least four condensed rings. The 6 er et 208/ catalytic cycle stock fraction may be dewaxed before addition FOREIGN PATENTS to the mineral base oil, and the resultant blend may be treated 8,221 9/1958 Germany 208/14 with activated earth for additional color and oxidation stabilil,8l3,542 7/1969 Germany 208/14 y p o e t- MA KE-UP SOLVENT L WATER SOLVENT STRIPPER 34 NAPMTHENIC CRUDE 56 mxmc 57 z zone 32 ABSORPTION SOLVENT sx'rmcraou :a "time: ,1 DISTILLATION 47 zone 48 EXTRACT 3 muss ELECTRICAL 32 CATALYTIC l4 CYCLE srocx 2 oswaxme SOLVENT SOLVENT DISTILLATION zone DIS'HLLATION ZONE ELECTRICAL INSULATING OIL CONTAINING A IIYDROTREATED CATALYTICALLY CRACKED CYCLE OIL BACKGROUND OF THE INVENTION This invention relates to mineral oils used as electrical insuvoltage levels much higher than the voltages at which a transformer or switch is normally operated, since severe surges of voltage can occur in transformers and switches exposed to systemic disturbances such as lightning. This property of an insulating oil is termed its impulse strength. In addition, these oils must have an inherent resistance to oxidative processes which break down such oils and make then unfit for their intended purpose. With additive oxidation inhibitors, they should show a substantial increase in oxidative resistance over their inherent oxidative resistance.

Heretofore, insulating oils with acceptable impulse strengths but rather poor oxidative resistances have been produced from varied crude distillates or deasphalted raffinates by refining treatments which include acid refining, hydrogen refining, or solvent extraction plus hydrogen or acid refining. Recently, it was disclosed in U.S. Pat. No. 3,318,799 that the oxidative resistance of refined oils may be improved by the inclusion of up to about 5 weight percent of a hydrogen-treated heavy cycle gas oil from a catalytic cracking operation. However, the addition of such heavy cycle gas oils depresses the impulse strength of the refined oil to which it is added to levels that are unsuitably low for an insulating oil.

SUMMARY OF THE INVENTION By my invention, l have discovered a novel oil composition having both outstanding oxidative resistance and impulse strength. This oil is produced by combining, so as to form 100 parts by weight ofa blend, from about 80 to about 97 parts by weight of a mineral base oil usable as an electrical insulating oil, but deficient in oxidative resistance, with from about 20 to about 3 parts by weight of a catalytic cycle stock fraction boiling within the range from about 450 F. to about 690 F. and having a SO-percent distillation point of at least about 550 F. This particular light fraction of catalytic cycle stock, l have discovered, has no more than about 1.0 weight percent of aromatic hydrocarbon compounds having four or more condensed rings. Together, the blend of mineral base oil and this particular fraction of catalytic cycle stock has no more than about 22 weight percent total aromatic compounds and no more than about 0.10 weight percent of aromatic hydrocarbon compounds of at least four condensed rings. Before blending, the fraction of catalytic cycle stock in the mineral base oil is hydrogen refined for improved color and stability.

The oxidative resistance of the present oil is quite good, particularly its innate oxidative resistance (no added inhibitors) and its inhibitor responseits increase in oxidative resistance when inhibitors are added. lt has an ASTM D-1904 life in excess of 88 hours and an inhibited ASTM D-1904 life in excess of 500 hours, typically greater than 600 hours and in many cases up to more than 1,000 hours. In addition, the present oil will have a Doble Power Factor Valued Oxidation life exceeding 88 hours, or an ASTM D-1313 weight percent of sludge no greater than about 0.06, or an ASTM D-2440 weight percent sludge/neutralization value number no greater than 0.2/0.5 at 72 hours and 0.3/0.7 at 164 hours, or any combination or all of these performance characteristics. The present oil can have a modified ASTM D-943 life in excess of 100 hours, and in some cases more than 200 hours.

The present oil has an excellent impulse strength, particularly in view of its high resistance to oxidation. There presently is no standard industry test procedure for measuring the impulse strength of an insulating oil. Impulse strength was determined herein by finding the voltage level at which the oil would lose its insulator properties and permit an electric current to are through it between a grounded one-half inch diameter, polished brass sphere serving as a lower electrode and a Recoton phonograph needle vertically aligned one inch above the sphere and serving as an upper electrode, when a negative voltage wave was applied to the needle. The wave shape was not significantly different from the 1.2X50 usec. wave recommended by the IEEE Guide for Transformer Impulse Tests No. 93. Testing was started at a voltage below the expected impulse breakdown voltage. Three impulses were applied for each step; if no failure was obtained, the impulse voltage was increased by 10 kilovolts and the tests were repeated. This process was continued until a failure was obtained. After each failure, the procedure was repeated with a new needle and a new sample of oil from the same container. This procedure was continued until five failures had been obtained for each oil type. The sphere was replaced with a freshly polished sphere before testing a different oil. (The test method is more fully discussed by E. L. Raab and C. L. Kirk in an article entitled, Impulse Tests Reveal New Variables in Insulating Oil appearing in Electrical World, Apr. 7, 1969, at pages 38-40.) For commercial acceptability, an electrical oil must have an impulse strength of at least about kv., desirably greater than kv., and preferably at least kv. The present oil meets this requirement, showing an impulse strength as great as kv.

The mineral base oil of the present oil is any distillate or deasphalted raffinate which may suitably be used as an electrical insulating oil but which is deficient in oxidative resistance. Many such mineral base oils are commercially available. Typically, and as is well known in the art, the mineral base oil will have been treated to reduce its content of aromatic compounds, as by solvent extraction with sulfur dioxide, phenol, or furfural, or another suitable solvent, by acid treating, or by incomplete hydrogenation with a nickel or other hydrogenation catalyst, and it may have been hydrogen refined in the presence of a sulfur-resistant catalyst such as cobalt molybdate to improve color and to reduce the sulfur and nitrogen content of the distillate. Some mineral base oils will have been treated with activated earth to improve color and stabilization of the base oil. Preferably, the oil is derived from a naphthenic crude, suitably a coastal crude (e.g. Webster), so as to obtain a pour point in the final oil of at least about 40 F. or lower. For applications in which the pour point may be as great as 15 F., the distillate also may be derived from a mixed base or a paraffinic crude. The distillate will suitably have a viscosity at 100 F. within the range from about 50 to about 300 S.S.U., preferably within the range from about 55 to about 75 S.S.U., depending upon the design of equipment in which the oil is used. Flash point of the distillate will be at least about 265 F. and preferably at least about 295 F.

The catalytic cycle stock which is fractionated to obtain the particular fraction added to the mineral base oil in accordance with this invention is a product of catalytic cracking operations conducted upon heavy or high boiling petroleum fractions. Catalytic cracking decomposes the heavy petroleum fractions into several fractions: gases; volatile materials having the same boiling range as gasoline; a heavier, higher boiling fraction; and a residue of tars or coke. The heavier fraction boiling between the gasoline boiling range and the residue is known in the art as catalytic cycle stock, because it is norm ally recycled through the cracking system until it is completely converted to gasoline, although it is sometimes sold as a distillate or gas oil. It is very rich in aromatics and is thermally quite stable. Catalytic cycle stock characteristically has a density at 15 C. within the range from about 0.85 to about 1.100, a viscosity at 210 F. within the range from about 2 to about 8 centistokes, and an index of refraction measured at 67 C. within the range of from about 1.4900 to about 1.5500.

ln accordance with this invention, use is made of that fraction of a catalytic cycle stock which boils within the range from about 450 F. to about 690 F. and has a 50 percent distillation point of at least about 550 F. Preferably, the fraction has a boiling point no higher than about 660 F. This particular fraction, which may be called a light catalytic cycle stock fraction, has'a unique combination of ingredients which, when added in proper proportions to the aforesaid mineral base oil (suitable as an electricaloil but having a deficiency in oxidative resistance), improves the oxidative resistance of the oil without depressing its impulse strength to levels which would make it unfit for service as an electrical insulating oil. As aforesaid, this, light fraction has less than about 1.0 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, and preferably has less than about 0.5 weight percent, most desirably having at most about 0.2 weight percent or less, of such compounds.

Fractionation of a catalytic cycle stock to provide the unique combination of ingredients in the particular fraction of catalytic cycle stock used in this invention may be accomplished, as herein it was, by employing a vacuum distillation column containing 15 theoretical plates, with a 5:1 reflux ratio (hereinafter called 15/5 vacuum distillation constant boiling being maintained by reducing column pressure and/or increasing boiling flasktemperature, boiling points being corrected to 760 mm. Hg. Other methods of fractionation may be used, in accordance with the skill of the art, which reduce the presence of aromatic hydrocarbon compounds of at least four condensed rings to the levels herein described and which provide for the inclusion of other catalytic cycle stock ingredients boiling below about 690 F., as determined by a 15/5 vacuum distillation column.

7 The catalytic cycle stock fraction of this invention is hydrogen refined, before or after fractionation from the total catalytic cycle stock, and preferably before addition to the mineral base oil, but suitably in combination with the mineral base oil, to improve the color and stability of the fraction, the refinement reducing the content of olefin unsaturates, sulfur and nitrogen in the fraction. The hydrogen refining occurs in the presence of a sulfur-resistant hydrogen-refining catalyst under moderate hydrogen-refining conditions. Suitably, the sulfur-resistant catalyst containsat least one metallic component from the Groups Vl-B and VIII of the Periodic Table of Elements, existing as the sulfide or oxide thereof, and carried by a suitable base. Preferred catalysts include molybdena oxide on activated alumina, mixtures of cobalt oxides and molybdenum oxides and cobalt molybdate on activated alumina. Suitable other hydrogen-refining catalysts may be molybdenum disulfide, nickel-molybdenum, nickel-cobaltmolybdate, nickel-tungsten sulfide, and iron-cobalt molybdate deposited on suitable bases. Hydrogen-refining temperatures may range fromabout 400 F. to about 700 F., with preferred temperatures being from about 475 F. to about 630 F. Pressures may range from about 200 p.s.i.g. to about 1,000 p.s.i.g., with preferred pressures ranging from about 650 to about 750 p.s.i.g. Space velocities may range from about 0.1 to about 5.0 v./v./hr. with preferred space velocities ranging from about 1 to 2 v./v./hr. Hydrogen is suitably employed in a treat rate of from about 100 to about 5,000 s.c.f./bbl. with a preferred amount of hydrogen being from about 500 to about 600 s.c.f./bbl.

Before or after either the hydrogen-refining operation or the fractionation of the catalytic cycle stock, a dewaxing operation may be conducted on the present fraction of catalytic cycle stock with dewaxing solvents such as ketone-aromatic hydrocarbon mixtures, propane and the like. A preferred dewaxing solvent consists of 65 percent methyl ethyl ketone and 35 percent toluene. For a ketone-aromatic solvent, dewaxing temperatures may range from about 1 5 F. to about +20 F with solvent-to-oil ratios of from about 1.0 to about 5.0. Preferred temperatures are within the range of from about 0 F. to about 10 F and a preferred solvent-to-oil ratio is about 2.7. The dewaxing operation is conducted when it is necessary that the refined catalytic cycle stock fraction have a pour point less than about 0 F. The dewaxing treatment does not otherwise modify the properties conferred on the final blended oil by the refined catalytic cycle stock fraction.

The fraction of the catalytic cycle stock boiling below about 690 F., and preferably below about 660 F is added in amounts of from about 20 to about 3 parts with from about 97 to about parts of the mineral base oil usable as an electrical insulating oil but deficient in oxidative resistance, from about 7 to about 16 parts of the fraction being preferably combined with from about 93 to about 84 parts of the mineral base oil, in each case resulting in parts of the blend. The oil produced by the combination of the fraction and the mineral base oil has no more than about 22 weight percent of aromatic compounds, preferably no more than about 21 weight percent thereof, and contains no more than about 0.10 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, preferably less than about 0.06 weight percent thereof, and most desirably less than about 0.05 weight percent of such aromatic hydrocarbon compounds.

After the catalytic cycle stock fraction and the mineral base oil are blended together, the resultant oil is preferably treated with an adsorptive clay, either by clay contacting of by clay percolation, as well known in the petroleum process arts. Alternatively, the catalytic cycle stock fraction and the mineral base oil may be individually treated with adsorptive clay before being combined and blended together. The clays further improve the color and oxidative stability of the oil. Suitable industrial clays useful for clay contacting or clay percolation include activated earths such as Bennett-Clark natural clay and Attapulgus clay. In clay contacting, usually from about 0.05 to about 1.0 lb./gal. of adsorbent clay is contacted with the distillate oil at temperatures of about 250 F. Clay percolation generally utilizes from about 0.05 to about 1.0 lb./gal. of adsorbent clay, with percolation being carried out at temperatures of from about 60 F. to about 225 F.

The foregoing may be visualized to better advantage by reference to the drawing and a description of the manner in which I carry out my invention.

DESCRIPTION OF THE DRAWING The single FIGURE is a flow diagram of a preferred mode of performing the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawing, reference numeral 11 designates a broad boiling catalytic cycle stock introduced intov the system from a catalytic cracking operation which may be of the fluidized bed type or of the dispersed phase or transfer line reaction type. The stream has a distillation range between the boiling range of gasoline and that of residue materials, e.g. from about 390 F. to about 1,l00 F. Density and viscosity of the stream are within the ranges indicated hereinabove. The broad boiling catalytic cycle stock stream is narrowed to a desired viscosity range by introducing it into a distillation zone 12, suitably at least one fractionation column, which is equipped with a heating element 13 for volatilizing the charge, suitably a steam coil or a furnace. Distillation zone 12 is provided with structure such as plates or other packing for bringing liquid condensate and rising vapor into intimate counter current contact. An overhead fraction boiling below about 500 F. is removed by way of line 14. A bottom fraction boiling above about 900 F. is removed by way of line 15, and a catalytic cycle stock having a nominal viscosity at 100 F. of 75 S.S.U. is removed by way of line 16. A typical inspection of the catalytic cycle stock is shown below in table I.

TABLE I-INSPECTION DATA ON CYCLE STOCK Density at 15 C. 0.9]71 Flash Point (COC), F. 350 Viscosity at F., S.S.U. 52.7

CS at2l0 F.,S.S.U. 36.4

Refractive Index at 67 F. 1,504 Pour 80 F.+ Color, Tag Robinson Silica gel Aromatics, w% 395 Saturates, w% 59.] Sulfur, wii 0.632

denum oxide. Hydrogen is introduced into the hydrogen-refin- 1 ing zone 17 through line 19 controlling by valve 20 to provide a hydrogen-treat rate between about 500 and 600 s.c.f./bbl., e.g. about 590 s.c.f./bbl. of the feed to the hydrogen-refining zone. The charge from line 16 is passed through zone 17 at a space velocity between about 1 and 2 v./v./hr., e.g. about 1 v./v./hr., at a temperature within the range from about 475 to about 630 F., e.g. about 525 F., and at a pressure within the range from about 650 to about 750 p.s.i.g., e.g. about 740 p.s.i.g. Hydrogen consumption is from 2 to 50 s.c.f./bbl. The

hydrogen-refined product discharges from zone 18 by way of line 21, and after suitable cooling and fractionation to remove light products and treatment for removal of hydrogen sulfide, is discharged into a solvent dewaxing zone 22 into which a dewaxing solvent, preferably 65 percent methyl ethyl ketone and 35 percent toluene, is introduced by way of line 23. In the dewaxing zone the solvent mixture is contacted with the hydrogen-refined catalytic cycle stock distillate at a solventto-oil ratio of 2.7 and a temperature of about 6 F., resulting in precipitation of wax which is discharged by way of line 24.

The dewaxed hydrogen-refined catalytic cycle stock distillate discharges from zone 22 by way of line 25 into a solvent removal zone 26 with solvent being discharged therefrom by line 27. The dewaxed hydrogen-refined catalytic cycle stock distillate then discharges from zone 26 by way of line 28 controlled by valve 29.

A typical gas chromatographic distillation of a dewaxed hydrogen-refined catalytic cycle stock distillate from line 28 shows the volume percents distilled at the respective temperatures indicated below in table II.

FEfifibdeT 5 00 prog ramnied t mperature chromatograph using thcrm istor-type detector, with a 6 ft.X inch column packed with 0.5 percent of 85-30 on Chromosorb W. 813-30 is a dimethyl poly-syloxane marketed by Dow-Corning Corp. and Chromosorb W is small particles of treated and purified diatomaceous earth sold by Johns-Manville Products Corporation.

The dewaxed hydrogen-refined catalytic cycle stock distillate from line 28 is charged into a distillation zone 30, which may be similar to distillation zone l2Twith a heating element 31, for imparting volatilizing temperatures to the feed from line 28. Preferably, zone 30 is a /5 vacuum distillation column. lnaccordance with the present invention, the catalytic cycle stock distillate is fractionated in distillation zone 30, the fraction of the stock boiling below about 690 F. (corrected to atmospheric pressure), preferably below about 660 F., being removed overhead by line 32, the heavier fractions being discharged by way of line 33.

A gas chromatographic distillation curve of a typical hydrogen-refined dewaxed catalytic cycle stock fraction of the present invention, in this case one fractionated at 657 F. on a 15/5 vacuum distillation column, shows the volume percents distilled at the respective temperatures indicated in table 111.

TABLE lIlGAS CHROMATOGRAPHIC DlSTlLLATlON OF CYCLE STOCK FRACTION Volume Distilled at Temperatures, F.

Same instrument as in Table 11,

The overhead fraction boiling below 690 F., preferably below 660 F. and having a 50 percent distillation point of at least 600 F., actually 619 F., is carried by line 32 into a mixing zone 34 where it is blended with a refined mineral base oil from line 56.

The refining of the mineral base oil is accomplished by charging a suitable crude oil, preferably a naphthenic crude, through line 35 into a distillation zone 36 having a heating element 37, as in the cases of distillation zones 12 and 30, with which distillation zone 36 may be similar. Light fractions boiling below about 295 F. are removed from the distillation zone 36 by way of line 38, and heavier fractions, for example, those boiling above about 900 F. preferably boiling above about 725 F., are taken off by way ofline 39. An intermediate fraction is withdrawn by way of line 40 and discharged into a r arbgeh afirrrrg'iaanarrating bean bra hya'ragen refining catalyst such as a 3.7 percent cobalt oxide and a 13.1 percent molybdenum oxide on activated alumina. Hydrogen is introduced into zone 41 through a line 43 controlled by a valve 44 to provide a preferred hydrogen-treat rate within the range from about to about 1,000 s.c.f./bbl., for example, about 300 s.c.f./bbl. of distillate. Other preferred hydrogenrefining conditions in zone 41 include a space velocity within the range from about 1 to about 2 v./v./hr., for example about 1.46 v./v./hr.; a temperature within the range from about 525 to about 630 F., for example about 600 F.; a pressure within the range from about 650 to about 750 p.s.i.g., for example about 710 p.s.i.g. Hydrogen consumption is from about 2 to about 15 s.c.f./bbl. The hydrogen-refined distillate discharges from zone 41 by way of line 45 into a solvent extraction zone 46, preferably a countercurrent multiple stage liquid-liquid extraction zone, into which a solvent having a preferential selectivity for relatively more paraff'rnic type constituents is introduced by way of line 47. Suitable solvents include phenol, sulfur dioxide, furfural, cresol, aniline, nitrobenzene, dimethyl sulfoxide, B 6 dichloroethyl ether, and the like as known in the art. Preferably, the solvent mixture is contacted with the hydrogen-refined distillate at temperatures within the range from about F. to about 6 F., at a solvent-to-oil ratio preferably of about 1.521, producing a raffinate phase and an extract phase. The extract phase is discharged by way of line 48 for removal of solvent and further processing as desired. The raffinate phase is discharged by line 49 into a solvent stripper S0 for removal of solvent from the raffinate phase by line 51 for recycling to line 47. Makeup of the solvent may be introduced into line 51 by line 52 controlled by valve 53, and water may be added to line 51 by line 54 controlled by valve 55. The solvent-free raffinate discharges by line 56. A typical inspection of a raffinate (mineral base oil) from a naphthenic crude distillate is shown in table IV.

TABLE IV-INSPECTION DATA ON MINERAL BASE OIL From line 56, the raffmate (or mineral base oil) is charged to mixing zone 41, where from about 80 to about 97 parts of the raffinate are blended with from about 20 to about 3 parts of the overhead fraction of the hydrogen-refined, dewaxed catalytic cycle stock distillate from line 32, resulting in 100 parts of blend. The blend from mixing zone 33 is discharged by line 57 into an adsorption zone 58 provided with a fixed bed 59 of an adsorbent clay, suitably a fullers earth or bleaching clay, e.g. Attapulgus clay. From about 0.05 to about 1.0 lb./gal. of adsorbent clay is contacted with the oil at temperatures within the range from about 0 to about 120 F. The oil withdrawn from bed 59 by line 60 is produced in accordance with this invention and is suitable for use as an electrical insulating oil.

The oil of this invention is described in greater detail in the following examples, which are set forth to further illustrate the invention, and not to limit the scope of the invention which is hereinafter defined by the appended claims.

EXAMPLES l-16 The electrical insulating oil of the present invention is illustrated by the examples set forth in table V hereinafter. Each of the examples is an oil composed of varying proportions of a mineral base oil and a whole or an undercut fraction of a hydrogen-refined dewaxed catalytic cycle stock with a nominal viscosity at 100 F. of about 75 S.S.U., abbreviated l-IRDW 75 Cycle Stock in table V. (As used herein, the term undercut fraction means the lower boiling portion of an oil which remains after the higher boiling constituents have been removed, e.g. by distillation.) The mineral base oil is a hydrogen-refined solvent extracted naphthenic Coastal distillate having inspection data as shown in table IV. The oil has an impulse strength of 186 kv., but is deficient in oxidative resistance. The hydrogen-refined dewaxed catalytic cycle stock utilized had a gas chromatographic distillation curve similar to that shown in table II. In examples 1-15, fractions of the catalytic cycle stock were undercut in a /5 vacuum distillation column at temperatures ranging from 649 F. to about 730 F. corrected to atmospheric pressure. In example 16, whole (uncut) catalytic cycle stock is used. In examples 1-8, 15 and 16, the mineral base oil is whole and uncut. In examples 9-l0, the mineral base oil is a heart-cut left after topping and undercutting the whole mineral base oil.

Impulse strength and oxidative resistance of the oils of examples 1-16 are shown in table I. Impulse strength was tested with a negative voltage wave as hereinbefore described Oxidative resistance was tested by ASTM tests D-1313, D-l904, D-2440, and modified ASTM tests D-943 and D-21l2. In modified test D-943, .as adapted to a transformer oil, the test is terminated when the acid number reaches 0.3 mg. of KOH per gram of oil, or when the interfacial tension of the oil (as determined by ASTM tests D-971 or D-2285) falls to 15.0 dynes per cm. or less. In modified test D-2l 12, the oil contains no inhibitor, and a bath temperature of 150 C. is used. ASTM D-l904 tests were run with and without added inhibitors (0.15 weight percent di-, tert-, butylparacresol) in the blended oil. Power Factor Valued Oxidation tests (PFVO) 5 developed by Doble Engineering Company of Belmont, Massachusetts were also conducted. PFVO tests are an extension of the Doble Oxidation Test described in ASTM Standards on Electrical insulating Liquids and Gases," pp. 307-313, Dec. 1959, under the title Suggested Method of Test for Oxidative Characteristics of Mineral Transformer Oil." The PFVO test determines the power factor of the oil at two hour intervals throughout the oxidation period. A curve is obtained by plotting the power factor against the oxidation time..The test is terminated, as in ASTM D-l 904, either when the sludge is first detected or when the acid number exceeds 0.25 mg. KOH per gram of oil, or it may be terminated when the power factor of the oil exceeds an empirically determined set of values. Inspections were made on the oils by the standard methodspf ASTM D 287, D-445, and D-l56.

Table V shows the criticality of obtaining the proper fraction of catalytic cycle stock to prepare an oil blend having both a high impulse strength and a high oxidative resistance. Table V shows that such oils are made from a mineral base oil, suitable as an electrical insulating oil but for a deficiency in oxidative resistance, and a hydrogen-refined catalytic cycle stock fraction boiling possibly above 700 F. but not as high as 729 F. or 730 F., and desirably no greater than 690 F., preferably below about 660 F., but above 500 F.

The compositions of the components of the oils of examples 1-3, 15 and 16 (more particularly, the compositions of the whole mineral base oil, the whole hydrogen-refined dewaxed catalytic cycle stock and the cycle stock undercut at 730 F. and 649 F.) were determined by mass spectrographic analysis of the aromatics, saturates, and polars fractions of a silica gel separation of the component oils. The results of that analysis are shown in table V1.

TABLE VI HRDW 75 c.

Baislo Undercut atwhole Whole 730 F. 649 F.

Total aromatics 44. 18 47. 015 63. 64

l-rlng aromatics. 10. 137 2. 502 2. 835 5. 360

241mg aromatics. 4. 980 10. E13 14. 900 31. 862

3-ring aromatics 0. 189 20. 478 21. 257 10.282

4-ring aromatics 0. 031 6. 132 3. 813 0. 178

ii-ring aromatics... 0.001 0. 188 0. 086 0. 000 6-ring aromatics 0.001 0. 045 0. 0 0. 0

Post G-ring aromatics 0.0 0. 0 0. 0 0. 0

Thiophenes 0.006 2. 659 2. 472 3. 136 Furans. 0. 056 1. 665 1. 689 2. 821

Total saturates 84.400 51. 68 49. 55 44.84

Total naphthenes. 78. 154 34. 780 32.884 27.862

Total sulfur 0. 012 0. 59 0. 554 0. 463

'Total nitrogen, p.p.m.. 1. 0 580. 0 610. 0 420.0 Polar fraction 0.200 4. 14 3. 40 1. 52

Table VI shows that the whole hydrogen-refined catalytic cycle stock contained substantial amounts of aromatic hydrocarbon compounds with four or more rings, that undercutting the cycle stock at a temperature of 730 F. reduced the concentration of such aromatic hydrocarbon compounds by about one-half, but that undercutting the cycle stock at 649 F. reduced the concentration of such aromatics by well over more than an order of magnitude.

From the constituent values set out in table V1, the weight percent of total aromatic compounds (including hydrocarbon Q95 5 on 8 3325 3523 5 2: an; 5 5520 WEE, in n: 3 .8 3 n Fm B3 3 Dwm E. 25 5 x 2 5 $23 QEEEWQ 385 Jam}: a a M 925 3 032083 395 83:35

2 on 55: $5-0 2.54 H 595 Nam n2 35 S83 85%; D 88 d oQac o no dbo 0 ma 085 0 min 63 8 o as d\s c no 038 o 3 035 o 3 63 0 no 638 o me 326 h 003 3 uafiouc .........1.I.....ll...12222511---..@235 xogm 20R. 3 M .1.-. 3 8E? 82: E am m a e 2 0 A2onB- a. 32m "2633 8363800 aromatics, thiophenes and furans) and the weight percent of aromatic hydrocarbon compounds having at least four condensed rings, were determined for examples l-3 and 15, 16. These are set out in table Vii.

fraction of this invention may be added to the mineral base oil, so long as the total concentration of all aromatic compounds does not exceed about 22 weight percent.

EXAMPLES 17-24 TABLE VII The improved oxidative resistance of the present high im Example No 1 2 3 1 pulse strength oil is illustrated by comparison of impulse Composition percent, strengths and oxidative resistances obtained for a variety of Base 011 (whole) 90 86 79 79 93 1O transformer oils identified as examples 17-25 and composed a fi i fff f fi i 7 as set out in table Viii hereinafter, the same tests being used for impulse strengths and oxidative resistances as in examples 7 l-l6. figgfig wt In table V111, examples 17-20 are transformer oils manufacperceqt 19 22 20153 23 43 22047 11415 15 tured and marketed by major oil companies. Examples 17-19 g g gggg g f are acid treated oils, and example is a hydrogen-treated oil.

percent .iml 0.0415 0.0533 0, 3 4 ,4 These oils contain no catalytic cycle stock. Impulse Strength! 156 150 135 112 125 Examples 21-25 contain variously treated catalytic cycle stock. In addition, examples 23-25 contain minor amounts of Table v clearly shows the effect of aromatic compound 20 anthracene oil, which on mass spectrographic analysis was content on the impulse strength. It illustrates the deleterious fofmd to have perFem of hydrocarbon aromatics efi'ects which result from the presence of more than about 22 with fourlor more cqndenged "9 f h f l 20 weight percent aromatic compounds and more than about 0.1 ,Examp e 2 lfconslzts 0 9 t o i z weight percent aromatic hydrocarbon compounds having four hydni-re i :5: s or more condensed rings. Note that the oils of examples 1 and nmmal.vlscsny at T 15 I Cyc e 2 which are made vmh cycle stock fraction boiling below stock bolls over a gas chromatographic distillation range from o o F. and which have suitable impulse strengths, have a full order f to 996 and has a 50 percent dlsunauon of of magnitude less or aromatic hydrocarbon compounds of E l 22 24 b th me ndercut four or more condensed rings than do either the oil of example xamp es as a ase e s3 u 15 which is made up with cycle stock undercut at 730F or mineral base on as examples 11-14 exarilple 25 usmg thc oil of example 16 which is made p with whole c;cle whole (uncut) mineral base oil. The catalytic cycle stock used stock. However, example 3 of table V11 shows that desired imm f a 22-24 56, 3 pulse strengths are not obtained even at the reduced four-ring avmg a {101mm vlscosl y a o l aromatics content if the total content of all aromatic coma boning range slmllar to that of i cycle stock used m pounds in the blended oilistoo high. The maximum permissi- F i cyciethstock r i 22 i ble content of total aromatic compounds is possibly above 22 i a areas f e YF stole m gf e I weight percent, but 22 weight percent appears to be about the ewaxe an y rogcn re me e We c stoc. o "T e upper limit and 21 weight percent or less is desirable The is uzrcut diwaxed (not hydrogen refined) nominal 75 viscosity c e stoc maximum content of aromatic hydrocarbon compounds of Cy four or more rings may possibly be above 0.10 weight percent, in gz z zffix gl gizgfg g i 2:33: 2:- but weight percent appears to be about the upper limit, blend at 53 9 F then into blendg y addeg and preferably is as small as possible less than about anthracene oil, followed by hydrogen refining the mixture at 0.055 weight percent. The catalytic cycle stock fraction which F. after which the mixture was pucolated through Ab :z g pgesem g g have as mucdh f tapulgus clay at the rate of 0.5 lb./gal. The oil of example 24 I i Pew d o :Q i, d f gl f s o at was prepared by first blending anthracene oil with the mineral $112322? ."fZbrZ'"v ii J1m 5212321222331??? P :1; TH: E 5; 1;

owe y a mixing step in w ic y rogen-re me ewaxe hydrocarbon aromatlcshavlng four or more condensed rings, catalytic cycle Stock was mixed into the h drog fi cd it IS possible that 20 weight percent or more of the cycle stock blend f base i d anthracene i TABILE vrn Example No 17 1s 19 20 21 22 23 24 25 Composition, percent:

Acid treated oil A 100 Acid treated oil B Acid treated 011 C Hydrogen treated oil D. HRDW 150 cycle stock Base 011 (whole) Undercut, 729 F Anthracene oil I Inspections:

Gravity, API Viscosity, 100 F SSU Color, ASTM- Impulse strength,

Oxidation resistance:

AS'I'M D-1313 (bomb sludge) percent. 0 026 0. 04 PFVO 111e, hrs ASTM D-190411Ie, hrs 88 72 Neut. No./sludge at 88 hrs 0.12/mod. 0 30/neg 0 13/mod Inhibited ASTM D-1904 life, hrs 533 5 ASTM D-2440:

Sludge percent/neat. No. at-

72 hrs 0 12/0. 65 0 03/0. 11 0. 04/0. 16 64 hrs 1 0 25/0. 65 0 28/1. 12 0. 08/0. 18 I 336 hrs 0 35/0. 79 0 37/1. 23 0. 13/0. 24 Modified ASTM D-943, hrs 139 165 2 Modified ASTM D-2112, mlns 0. 16/tr 0 01/neg 0. 08/tl 0. 05/tr 0. 03/ncg. 0. 01/mod.

"X table vii illustrates, Ee acid-treated oils of examples 17-19 had very good impulse strengths, but their ASTM D-l904 uninhibited oxidative resistance lives were marginal. The hydrogen-treated oil of example 20 had improved ASTM D-l904 uninhibited life but a poor inhibitor response, as shown by inhibited ASTM d-l904 life. The oils of examples 2l25, containing various catalytic cycle stocks or fractions thereof boiling below about 730 F., some oils containing anthracene oil, all had depressed and unsuitably low impulse strengths. Some of the oils had unacceptably high ASTM d-2440values. None of the oils tested in examples 17-25 had both the high oxidative resistances and impulse strengths of the oils of examples l-lO, particularly oils of examples 1, 2, 5, 7 and 8, which represent preferred embodiments.

Having fully described the improved electrical insulating oil and the manner of making it involved in my invention, and having disclosed the preferred embodiments thereof, there will now be apparent various modifications or changes which will nonetheless be within the spirit and scope of my invention, as claimed.

I claim:

1. An electrical insulating oil, comprising, per I00 parts by weight:

a. from about 80 to about 97 parts ofa mineral base oil usable as an electrical insulating oil but deficient in oxidation resistance, and

b. from about 20 to about 3 parts of a hydrogen-refined catalytic cycle stock fraction boiling within the range from about 450 F. to about 690 F., with a 50 percent distillation point of at least 550 F., and having no more than about 1.0 weight percent of aromatic hydrocarbon compounds of at least four condensed rings,

said electrical insulating oil having an aromatic compound content no greater than about 22 weight percent and having no more than about 0.1 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, and having a satisfactory oxidation resistance and an impulse strength of at least about 140 kv.

2. The electrical insulating oil of claim 1 in which from about 93 to about 84 parts of said mineral base oil are combined with from about 7 to about 16 parts of said catalytic cycle stock fraction, said electrical insulating oil having an aromatic compound content no greater than about 21 weight percent and having nor more than about 0.06 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, said oil having a satisfactory oxidation resistance and an impulse strength of at least 145 kv.

3. The oil of claim 2 in which said catalytic cycle stock fraction boils within the range from about 500 F. to about 660 F.

4. The oil of claim 3 which has an ASTM D-1904 life of at least about 88 hours and an ASTM D-l904 inhibited life of at least about 600 hours.

5. The oil of claim 3 having an ASTM D-l3l3 sludge no greater than 0.06 weight percent.

6. The oil of claim 3 having a Power Factor Valued Oxidation life of at least 88 hours.

7. The oil of claim 3 having an ASTM D-2440 weight percent sludge/neutral number no greater than 0.2/0.5 at 72 hours and 0.3/0.7 at 164 hours.

8. The oil of claim 3 having a modified ASTM D-943 life of at least 120 hours.

9. An electrical insulating oil, comprising per 100 parts by weight:

a. from about 80 to about 97 parts of a mineral base oil usable as an electrical insulating oil but deficient in oxidation resistance, and having a flash point greater than about 265 F. and a pour point no greater than about 15 F., and

b. from about 20 to about 3 parts of a hydrogen-refined, dewaxed catalytic cycle stock fraction boiling within the range from about 500 F. to about 660 F., and having a 50-percent distillation point of at least 600 F., said fraction possessing no more than about 1.0 weight percent of aromatic hydrocarbon compounds of at least four condensed rings,

said electrical insulating oil having no more than about 21 weight percent of aromatic compounds and no more than about 0.05 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, said oil having an ASTM D-l904 life of at least about 88 hours, an ASTM D-l904 inhibited life of at least about 600 hours, and an impulse strength of at least about 145 kv.

10. The oil of claim 9 having a pour point of at least 40 F.

11. The oil of claim 10 having an ASTM color no greater than 0.5.

12. A method of preparing an electrical insulating oil comprising:

a. fractionating a catalytic cycle stock having a density of 15 C. offrom about 0.85 to about 1.10 g./cc., a viscosity of 210 F. of from about 2 to about 8 centistokes, and a distillation range between about 390 F. and l,l00 F. to obtain the fraction thereof boiling within the limits from about 450 F. to about 690 F., and having a 50 percent distillation point of at least 550 F.,

b. refining said catalytic cycle stock with hydrogen in a hydrogen-refining zone in the presence of a sulfur-resistant hydrogen-refining catalyst under hydrogen-refining conditions,

said steps (a) and (b) being conducted in any order, and

c. mixing from about 3 to about 20 parts by weight of the hydrogen-refined catalytic cycle stock fraction with from about 97 to about parts of a mineral base oil usable as an electrical insulating oil, but deficient in oxidation resistance, so as to produce 100 parts of a blended electrical insulating oil having no more than about 22 weight percent of aromatic compounds and no more than about 0.10 weight percent ofaromatic hyrdocarbon compounds of at least four condensed rings.

13. The method of claim 12 further comprising solvent dewaxing said catalytic cycle stock prior to step (c).

14. The method of claim 12 in which said catalyst is selected from a sulfide or oxide of at least one metallic element of Groups Vl-B and VII] of the Periodic Table of Elements and wherein said hydrogen-refining conditions include:

a temperature within the range from abo ut toabout a pressure within the range from about 500 to about 1,000

p.s.|.g.,

a space velocity within the range from about 1 to about 2 v./v./hr., and

a hydrogen-treat rate within the range from about 100 to about 1,000 s.c.f./bbl.

15. The method of claim 12 further comprising percolating said electrical insulating oil over an activated earth adsorbent at a rate of from 0.05 to about 1.0 lb./gal. at a temperature within the range from about 65F. to about 225 F.

16. In the method of preparing an electrical insulating oil wherein a mineral oil base usable as an electrical insulating oil but deficient in oxidation resistant is improved in oxidation resistance by the addition of a hydrogen-treated catalytic cycle stock having a density at 15 C. within the range from about 0.85 to about 1.10 g./cc., a viscosity at 210 F. within the range from about 2 to about 8 centistokes, and a distillation range from about 390 F. to about 1,100 F., the improvement which comprises:

before addition of said catalytic cycle stock, fractionating said catalytic cycle stock to obtain the fraction thereof boiling within the limits from about 450 F. to about 690 F. with a 50-percent distillation point of at least 550 F. and containing no more than 1.0 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, and thereafter adding catalytic cycle stock fraction to said mineral base oil in a proportion whereby said electrical insulating oil contains less than 22 weight percent of aromatic compounds and less than 0.1 weight percent of aromatic hydrocarbons having at least four condensed rings, whereby said electrical insulating oil will have an impulse strength of at least kv. 17. The method of claim 16 in which said fraction of catalytic cycle stock in said electrical insulating oil is hydrogen refined.

18. The method of claim 17 in which from about 3 to about 20 parts of said fraction are combined with from about 97 to about 80 parts of said mineral base oil so as to produce 100 parts of said electrical insulating oil.

19. The method of claim 18 in which from about 7 to about 16 parts of said fraction are combined with from about 93 to about 84 parts of said mineral base oil so as to produce 100 parts of an electrical insulating oil having no more than about 0.06 weight percent of aromatic hydrocarbon compounds of at least four condensed rings and no more than about 21 weight percent of aromatic compounds, said electrical insulating oil having an improved oxidation resistance and an impulse strength of at least 145 kv.

20. The method of claim 16 in which said fraction boils within the range from about 500 F. to about 660 F. and has a 50 percent distillation point of at least 600.

21. The method of claim 20 in which from about 7 to about 16 parts of said fraction are combined with from about 93 to about 84 parts of said mineral base oil so as to produce parts of an electrical insulating oil having no more than about 0.05 weight percent of aromatic hydrocarbons of at least four condensed rings and no more than about 21 weight percent of aromatic compounds, said electrical insulating oil having an improved oxidation resistance and an impulse strength of at least kv. 

2. The electrical insulating oil of claim 1 in which from about 93 to about 84 parts of said mineral base oil are combined with from about 7 to about 16 parts of said catalytic cycle stock fraction, said electrical insulating oil having an aromatic compound content no greater than about 21 weight percent and having nor more than about 0.06 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, said oil having a satisfactory oxidation resistance and an impulse strength of at least 145 kv.
 3. The oil of claim 2 in which said catalytic cycle stock fraction boils within the range from about 500* F. to about 660* F.
 4. The oil of claim 3 which has an ASTM D-1904 life of at least about 88 hours and an ASTM D-1904 inhibited life of at least about 600 hours.
 5. The oil of claim 3 having an ASTM D-1313 sludge no greater than 0.06 weight percent.
 6. The oil of claim 3 having a Power Factor Valued Oxidation life of at least 88 hours.
 7. The Oil of claim 3 having an ASTM D-2440 weight percent sludge/neutral number no greater than 0.2/0.5 at 72 hours and 0.3/0.7 at 164 hours.
 8. The oil of claim 3 having a modified ASTM D-943 life of at least 120 hours.
 9. An electrical insulating oil, comprising per 100 parts by weight: a. from about 80 to about 97 parts of a mineral base oil usable as an electrical insulating oil but deficient in oxidation resistance, and having a flash point greater than about 265* F. and a pour point no greater than about 15* F., and b. from about 20 to about 3 parts of a hydrogen-refined, dewaxed catalytic cycle stock fraction boiling within the range from about 500* F. to about 660* F., and having a 50-percent distillation point of at least 600* F., said fraction possessing no more than about 1.0 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, said electrical insulating oil having no more than about 21 weight percent of aromatic compounds and no more than about 0.05 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, said oil having an ASTM D-1904 life of at least about 88 hours, an ASTM D-1904 inhibited life of at least about 600 hours, and an impulse strength of at least about 145 kv.
 10. The oil of claim 9 having a pour point of at least -40* F.
 11. The oil of claim 10 having an ASTM color no greater than 0.5.
 12. A method of preparing an electrical insulating oil comprising: a. fractionating a catalytic cycle stock having a density of 15* C. of from about 0.85 to about 1.10 g./cc., a viscosity of 210* F. of from about 2 to about 8 centistokes, and a distillation range between about 390* F. and 1,100* F. to obtain the fraction thereof boiling within the limits from about 450* F. to about 690* F., and having a 50 percent distillation point of at least 550* F., b. refining said catalytic cycle stock with hydrogen in a hydrogen-refining zone in the presence of a sulfur-resistant hydrogen-refining catalyst under hydrogen-refining conditions, said steps (a) and (b) being conducted in any order, and c. mixing from about 3 to about 20 parts by weight of the hydrogen-refined catalytic cycle stock fraction with from about 97 to about 80 parts of a mineral base oil usable as an electrical insulating oil, but deficient in oxidation resistance, so as to produce 100 parts of a blended electrical insulating oil having no more than about 22 weight percent of aromatic compounds and no more than about 0.10 weight percent of aromatic hyrdocarbon compounds of at least four condensed rings.
 13. The method of claim 12 further comprising solvent dewaxing said catalytic cycle stock prior to step (c).
 14. The method of claim 12 in which said catalyst is selected from a sulfide or oxide of at least one metallic element of Groups VI-B and VIII of the Periodic Table of Elements and wherein said hydrogen-refining conditions include: a temperature within the range from about 400* F. to about 650* F., a pressure within the range from about 500 to about 1,000 p.s.i.g., a space velocity within the range from about 1 to about 2 v./v./hr., and a hydrogen-treat rate within the range from about 100 to about 1,000 s.c.f./bbl.
 15. The method of claim 12 further comprising percolating said electrical insulating oil over an activated earth adsorbent at a rate of from 0.05 to about 1.0 lb./gal. at a temperature within the range from about 65* F. to about 225* F.
 16. In the method of preparing an electrical insulating oil wherein a mineral oil base usable as an electrical insulating oil but deficient in oxidation resistant is improved in oxidation resistance by the addition of a hydrogen-treated catalytic cycle stock having a density at 15* C. within the range from about 0.85 to about 1.10 g./cc., a viscosity at 210* F. within the range from about 2 to about 8 centistokes, and a distillation range from about 390 F. to about 1,100* F., the improvement which comprises: before addition of said catalytic cycle stock, fractionating said catalytic cycle stock to obtain the fraction thereof boiling within the limits from about 450* F. to about 690* F. with a 50-percent distillation point of at least 550* F. and containing no more than 1.0 weight percent of aromatic hydrocarbon compounds of at least four condensed rings, and thereafter adding catalytic cycle stock fraction to said mineral base oil in a proportion whereby said electrical insulating oil contains less than 22 weight percent of aromatic compounds and less than 0.1 weight percent of aromatic hydrocarbons having at least four condensed rings, whereby said electrical insulating oil will have an impulse strength of at least 140 kv.
 17. The method of claim 16 in which said fraction of catalytic cycle stock in said electrical insulating oil is hydrogen refined.
 18. The method of claim 17 in which from about 3 to about 20 parts of said fraction are combined with from about 97 to about 80 parts of said mineral base oil so as to produce 100 parts of said electrical insulating oil.
 19. The method of claim 18 in which from about 7 to about 16 parts of said fraction are combined with from about 93 to about 84 parts of said mineral base oil so as to produce 100 parts of an electrical insulating oil having no more than about 0.06 weight percent of aromatic hydrocarbon compounds of at least four condensed rings and no more than about 21 weight percent of aromatic compounds, said electrical insulating oil having an improved oxidation resistance and an impulse strength of at least 145 kv.
 20. The method of claim 16 in which said fraction boils within the range from about 500* F. to about 660* F. and has a 50 percent distillation point of at least
 600. 21. The method of claim 20 in which from about 7 to about 16 parts of said fraction are combined with from about 93 to about 84 parts of said mineral base oil so as to produce 100 parts of an electrical insulating oil having no more than about 0.05 weight percent of aromatic hydrocarbons of at least four condensed rings and no more than about 21 weight percent of aromatic compounds, said electrical insulating oil having an improved oxidation resistance and an impulse strength of at least 150 kv. 